The present invention relates to a motor driving apparatus and a method for control of motor revolution and relates to a technique that is effectively used as a revolution control technique for a three-phase spindle motor of a hard disk drive (HDD), for example.
For driving the spindle motor of an HDD system, a soft switching method is used in which PWM is performed for two phases during current-conducting phase switching to suppress a steep change in current. In order to rotate a motor, detecting the motor position is needed. As a sensor-less method, it is known that the back electromotive force (BEMF) of the motor is detected during a non-conducting period following the current-conducting phase switching. Detecting zero crossing of an inductive load current is described in Japanese Unexamined Patent Publication No. Hei 10 (1998)-341588. A motor driving device and an integrated circuit device for motor driving adapted to reduce a variation in motor running torque are described in Japanese Unexamined Patent Publication No. 2005-102447.
The above Patent Document 2 was previously proposed by the present inventors. To solve problems in the above Patent Document 1 and the like, in Patent Document 2, output voltages are supplied to three-phase coils by a three-phase DC motor output stage including a predriver for supplying drive voltages to power MOSFETs. Current zero crossing detection is performed by monitoring whether the gate-source voltage of each of the power MOSFETs is equal to or greater than a predetermined voltage. Output of the current zero crossing detection is used for PLL control whereby the timing of current-conducting phase switching is controlled and a drive voltage with 180 degree (deg) conduction is created. The three-phase DC motor output stage including the predriver for supplying drive voltages to the power MOSFETs supplies the output voltages to the three-phase coils. In particular, it generates sinusoidal drive voltages with a waveform pattern in which a down hook for a lowest voltage phase which corresponds to GND and an up hook for a highest voltage phase which corresponds to power supply alternate per electric angle of 60 degree, the waveform being represented by a combination of linear functions. Thereby, sinusoidal currents flow through the three-phase coils.
[Patent Document 1]
Japanese Unexamined Patent Publication No. Hei 10 (1998)-341588
[Patent Document 2]
Japanese Unexamined Patent Publication No. 2005-102447